Optical Tweezers for Force Measurement in Living Cells

Optical tweezers are used to manipulate microscopic objects and measure forces and displacements at the piconewton and nanometer scale. This is accomplished by tightly focusing a laser, which is capable of locally trapping objects. Measurements are often done with beads in simple viscous liquids, where calibration is relatively simple. However, in order to analyze the inner components of living cells (embedded in cytoplasm) with unknown optical and physical properties, new calibration methods for the optical tweezers must be used. Two methods of force calibration for intracellular measurements are the Photon Momentum Method and the Active-Passive Method. We are developing a system capable of using both calibration methods. This will enable us to precisely measure the force kinetics in the cytoplasm of living cells and quantify their mechanical activity. We are investigating the relationship between thermal and non-thermal fluctuations (an active non-equilibrium state). Once this relationship is quantified, it will provide insight on the basic physics of the biological processes occurring in living cells. We aim to use both calibration methods to verify accurate force measurements in living cells to characterize their non-equilibrium fluctuations.